avcodec/cavs: fix B_SUB_DIRECT col-MB is Intra MB case.

in this case current MB size is forced to 16x16 (AVS standard section 9.9.1)
Signed-off-by: Yao Wang <jiayaowang@gmail.com>
Fixes Ticket 1901
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/cavs.c

@@ -573,7 +573,7 @@ void ff_cavs_mv(AVSContext *h, enum cavs_mv_loc nP, enum cavs_mv_loc nC,
 
     mvP->ref  = ref;
     mvP->dist = h->dist[mvP->ref];
-    if (mvC->ref == NOT_AVAIL)
+    if (mvC->ref == NOT_AVAIL || (nP == MV_FWD_X3) || (nP == MV_BWD_X3 ))
         mvC = &h->mv[nP - 5];  // set to top-left (mvD)
     if (mode == MV_PRED_PSKIP &&
         (mvA->ref == NOT_AVAIL ||

libavcodec/cavsdec.c

@@ -805,6 +805,8 @@ static int decode_mb_b(AVSContext *h, enum cavs_mb mb_type)
         ff_cavs_mv(h, MV_BWD_X0, MV_BWD_C2, MV_PRED_MEDIAN, BLK_16X16, 0);
         break;
     case B_8X8:
+#define TMP_UNUSED_INX  7
+        flags = 0;
         for (block = 0; block < 4; block++)
             sub_type[block] = get_bits(&h->gb, 2);
         for (block = 0; block < 4; block++) {
@@ -812,11 +814,30 @@ static int decode_mb_b(AVSContext *h, enum cavs_mb mb_type)
             case B_SUB_DIRECT:
                 if (!h->col_type_base[h->mbidx]) {
                     /* intra MB at co-location, do in-plane prediction */
-                    ff_cavs_mv(h, mv_scan[block], mv_scan[block] - 3,
+                    if(flags==0) {
+                        // if col-MB is a Intra MB, current Block size is 16x16.
+                        // AVS standard section 9.9.1
+                        if(block>0){
+                            h->mv[TMP_UNUSED_INX              ] = h->mv[MV_FWD_X0              ];
+                            h->mv[TMP_UNUSED_INX + MV_BWD_OFFS] = h->mv[MV_FWD_X0 + MV_BWD_OFFS];
+                        }
+                        ff_cavs_mv(h, MV_FWD_X0, MV_FWD_C2,
                                    MV_PRED_BSKIP, BLK_8X8, 1);
-                    ff_cavs_mv(h, mv_scan[block] + MV_BWD_OFFS,
-                               mv_scan[block] - 3 + MV_BWD_OFFS,
+                        ff_cavs_mv(h, MV_FWD_X0+MV_BWD_OFFS,
+                                   MV_FWD_C2+MV_BWD_OFFS,
                                    MV_PRED_BSKIP, BLK_8X8, 0);
+                        if(block>0) {
+                            flags = mv_scan[block];
+                            h->mv[flags              ] = h->mv[MV_FWD_X0              ];
+                            h->mv[flags + MV_BWD_OFFS] = h->mv[MV_FWD_X0 + MV_BWD_OFFS];
+                            h->mv[MV_FWD_X0              ] = h->mv[TMP_UNUSED_INX              ];
+                            h->mv[MV_FWD_X0 + MV_BWD_OFFS] = h->mv[TMP_UNUSED_INX + MV_BWD_OFFS];
+                        } else
+                            flags = MV_FWD_X0;
+                    } else {
+                        h->mv[mv_scan[block]              ] = h->mv[flags              ];
+                        h->mv[mv_scan[block] + MV_BWD_OFFS] = h->mv[flags + MV_BWD_OFFS];
+                    }
                 } else
                     mv_pred_direct(h, &h->mv[mv_scan[block]],
                                    &h->col_mv[h->mbidx * 4 + block]);
@@ -832,6 +853,7 @@ static int decode_mb_b(AVSContext *h, enum cavs_mb mb_type)
                 break;
             }
         }
+#undef TMP_UNUSED_INX
         for (block = 0; block < 4; block++) {
             if (sub_type[block] == B_SUB_BWD)
                 ff_cavs_mv(h, mv_scan[block] + MV_BWD_OFFS,